Axial-piston machine



1968 D, KRATZENBERG ETAL 3,410,220

AXIAL-PISTON MACHINE Filed Nov. 30, 1966 2 Sheets-Sheet 1 fill 42 29c ,0 I 27 I I f I1 q I 291 :2 25 23 3 I .74 1 '1" V \A 5 2o j I T H. I H 6 v;fl}\ i 4 Q H F 42 18 I I /9 5 G. 8 A l 5b 7 I j I I I 15 8 q (L 7 F Dietrich Krafzenberg Franz Forster GercL Ahrens INVENTORS.

BY I

Nov. 12, 1968 Filed Nov. 30, 1966 D. KRATZENBERG ETAL AXIAL-PISTON MACHINE 2 Sheets-Sheet 2 Gerd Ahrens INVENTORS.

Attorney United States Patent 3,410,220 AXIAL-PISTON MACHINE Dietrich Kratzenberg, Haibach, Franz Forster, Karlstadt, and Gerd Ahrens, Hosbach, Germany, assignors to Linde Aktiengesellschaft, Wiesbaden, Germany, a corporation of Germany Filed Nov. 30, 1966, Ser. No. 597,944

Claims priority, application Germany, Dec. 1, 1965,

7 Claims. (Cl. 103162) ABSTRACT OF THE DISCLOSURE This disclosure is directed to the journaling of a cylindrical drum of an axial-piston hydraulic pump or motor in which a nonrotatable but axially shifta-ble central shaft rotatably carries the piston drum and bears axially thereupon (via an antifriction means) under hydraulic pressure developed in at least one chamber in the housing having an axially effective surface formed on the shaft.

Our present invention relates to hydraulic axial-piston machines and, more particularly, to the rotatable journaling of the piston drum of an axial-piston motor or pump.

In the commonly assigned U.S. Patents Nos. 3,261,421 and 3,279,173 and copending application Ser. No. 450,- 913, filed Apr. 26, 1965 (now U.S. Patent No. 3,299,635), there is described a class of axial-piston machines generally employed in hydrostatic hydraulic transmissions and mechanisms. Such machines comprise a rotatable cylinder drum journaled within a housing upon a fluidcontrol, fluid-distribution or valve plate, the angularly spaced annular array of cylinder bores in this drum slidably receiving respective pistons which co-operate :with a control flange or swash plate inclined to the axis of rotation of the drum so that, upon induced rotation of the drum, the pistons displace hydraulic fluid through the valve plate and the machine constitutes a hydraulic pump for use in systems of the type described in the aforementioned patents and copending application.

In a hydraulic motor of the axial-piston type, hydraulic fluid is forced into the cylinder bores and, by reaction of the piston against the control flange, rotation of the drum and a shaft coupled therewith (e.g., via the control flange) is carried out. Since the operating efiiciency of each of these hydrostatic machines is a function of the angle of inclination of the control flange to the axis of rotation of the drum, the systems are of particular suitability in variable-speed transmissions. Furthermore, since the hydrostatic pump and hydrostatic motor can be coupled via only two hydraulic lines over considerable distances, they can be used for remote indication and actuation, for servomechanisms, and for remote power transmission.

It has been the practice in some axial-piston machines of the general character described, to support the cylinder drum upon a stationary axial or central shaft rigid with the control or valve plate or some other portion of the housing. In order to hold the cylinder drum against this plate with forces increasing with the hydraulic pressures tending to separate the drum from the plate over which it slides, it was proposed to provide a chamber between the stationary support shaft and the drum with annular surfaces of the shaft and the drum receiving hydraulic force to urge the drum against its control plate. Considerable difiiculties are involved in this kinematic relationship since the bearings between the shaft and the drum must be capable of permitting axial movement as well as rotational movement. Furthermore, the two types of movement prevent adequate sealing of the chamber, and the supply of hydraulic fluid thereto in view of the rota- 3,410,220 Patented Nov. 12, 1968 tional and axial movement of the drum is rendered complex.

It is, therefore, the principal object of the present invention to provide an improved axial-piston machine in which these disadvantages are avoided.

Another object of this invention is to provide an improved method of rotatably supporting the cylinder drum of an axial-piston machine whereby the sliding of the device can be improved and pressure may be supplied to hold the drum against its control plate.

These objects and others which will become apparent hereinafter are attained, in accordance with the present invention, by an improved arrangement wherein, instead of being fixed with respect to the housing, the central shaft or axis of the cylinder drum is at least limitedly axially movable within and on the housing and is keyed thereto to prevent its rotation relative to the housing, While the housing structure (e.g., below the control or valve plate) forms with the shaft an annular compartment communicating with one side at least of the hydraulic system for applying hydraulic pressure in axial direction to a surface of the shaft effective so as to draw the cylinder drum against its control plate. When reference is made here to a control plate underlying the cylinder drum, it will be understood that this plate may be rotatable with the drum, in which case it is held thereby against the stationary portions of the housing which, in conventional manner, is formed with ports communicating with the apertures of the valve plate.

According to an important feature of this invention, antifriction means are provided in the thrust direction of the shaft between the latter and the cylinder drum for exerting the aforementioned axial force upon the latter. The antifriction means can include a roller or ball-type thrust bearing or lubricant-film bearings of a hydrostatic nature as will be described in greater detail hereinafter. The bearing means journaling the cylinder drum upon the shaft need not admit of relative axial motion of the shaft and the cylinder drum or may be restricted to a small degree of such relative motion since the shaft retains the. cylinder drum and the control plate against the housing.

Thus, the present system overcomes important disadvantages of the prior art in that it applies an axial force to the cylinder drum to press it against its control plate and to retain its control plate against the housing floor, while simplifying the sealing of the entire system and especially the pressure chamber at which the hydraulic force is supplied to the shaft.

According to a more specific feature of our invention, spring means are provided between the shaft and a spring seat to bias the cylinder drum against its control plate even when the hydraulic pressure delivered to the chamber falls off. Moreover, the chamber is advantageously constructed with a pair of annular compartments in which respective shoulders of the shaft are exposed, the hydraulic pressure within these compartments acting upon these shoulders in the same direction, i.e., to draw the axle and the cylinder drum against the control plate. Each of the compartments is, moreover, provided with a respective passage communicating between the inlet and outlet sides of the hydraulic system, respectively, and the individual chambers. Thus, at least one of these shoulders always receives the maximum pressure while the other receives the pressure at the outlet. Should the inlet pressure be increased and the outlet pressure be decreased or should the inlet pressure drop while the outlet pressure increases, substantially the same force Will be applied to the axially shiftable shaft.

When a hydrostatic bearing is provided between the free end of the shaft and the juxtaposed face of the cylinder drum, we prefer to provide the shaft with a pair of passages respectively communicating with the compartments and communicating with a further space around a collar or other annular bearing member or therewith, the hydraulic fluid being forced between this annular member and the face of the drum to form a lubricant film capable of acting as a thrust bearing. When a mechanical thrust bearing is employed, the outer disk member is engaged by the free end of the shaft, whereas the inner disk is urged into contact with the rolling element and against the fixed disk by a belleville or dished-spring arrangement.

Other objects, features and advantages of the present invention will become more readily apparent from the following description, reference being made to the accompanying drawing in which:

FIG. 1 is an axial cross-sectional view through a hydraulic axial-piston machine having mechanical forcetransmission means between the central shaft and the cylinder drum; and

FIG. 2 is an axial cross-sectional view through an axial piston machine employing hydrostatic force transmission.

In FIG. 1, we show a hydrostatic motor for use in a hydraulic transmission of the type described in the aforementioned copending application or issued patents, which comprises a driven shaft 50' carrying a control flange 8 such as that the axis A of the driven shaft intersects the axis A of the housing 1 at an obtuse angle a. The housing 1 of the hydraulic machine can be mounted upon a base plate or otherwise provided with support means for positioning it in relation to the driven system and/ or in relation to a hydrostatic pump whose swash plate or control flange is adjustable. In a kinematic reversal of the system, shaft 50 may be the driving shaft of a hydrostatic pump 'whose associated hydrostatic motor may have a s-wingable swash plate or control flange. The hydraulic machine, in either case, is provided with a central chamber 1 in the housing 1, within which a control or valve plate 2 is mounted for rotation about an axle or shaft 11.

The valve plate 2 is provided with kidney-shaped distribution apertures 3 of the type described in the aforementioned application and patents and commonly known in the art. The apertures 3 communicate with passages 4' extending axially in a cylinder drum 5 to the respective cylinder bores 4. A plurality of such bores is formed integrally in spaced relation about the shaft 11 in the cylinder drum and parallel to the axis A of rotation thereof. The bases 4 thus form an annular array of cylinders within which respective pistons 6 are slidable. The pistons 6 are joined flexibly to the control flange 8 via connecting rods 7. To this end, the rods 7 are formed with spheroidal heads 7' received in correspondingly shaped sockets 8' of the flange for freedom of movement relative thereto with at least two degrees of freedom. The sockets 8 are flared outwardly at 8" to clear the connecting rods 7 and preclude bending.

The apertures 3 of the control plate 2 register, upon rotation over the latter (or continuously register when the control plate 2 is stationary), with the axial passages 9 formed in the housing 1 axially beyond the cylinder drum 5. These passages 9 connect the apertures 3 with a pair of ports 10 which may be used interchangeably as the hydraulic inlet and hydraulic outlet of the machine depending upon the type of use to which it is put. Thus, when the system is operated as a pump, the left-hand port 10 (FIG. 1) can be considered the outlet whereas the other port is constituted as an inlet.

The central shaft or axle 11 is axially movable within the housing 1 (arrow 11) but is keyed to the housing, e.g., by splines 11" which prevent rotation of this shaft relative to the housing 1. An abutment flange 12 at the upper end of the housing 1 is formed on the axle shaft 11 and engages the end face 1" of the housing to limit the stroke of the shaft 11 in the direction opposite to arrow 11'.

At the lower or free end of the shaft 11, We provide a threaded portion 13 onto which a nut 14 is secured to retain a thrust-bearing ring 15, constituting one race of the bearing, upon the shaft 11. The other race-forming ring 16 bears axially against a shoulder 17 of the cylinder drum 5 within an axially open recess 51: at the free end of the shaft 11. The thrust bearing B, formed by the races 15 and 16 and the roller elements 15' is thus housed in this recess 5b. A further recess 5a extends axially inwardly from the recess 5b and forms an annular seat 18 for a dished-washer or belleville spring 19 which urges the ring 16 and bearing B, together with the shaft 11, axially downwardly while reacting against the cylinder drum 5 t0 yielda bly retain it against the control plate 2 and the floor 1b of the chamber 1 of housing 1. The means for rotatably mounting the cylinder drum 5 upon the axle 11 is here constituted by a pair of axially spaced needle bearings 20, respectively disposed close to the end of the drum 5.

The central shaft 11 is provided at its extremity remote from its free end with a pair of axially spaced annular shoulders 23 and 26 respectively forming with the housing 1 annular pressure chambers 24 and 26 behind the control plate 2. The shoulders 23 and 27 thereby constitute surfaces which, upon introduction of hydraulic medium under pressure, are effective to generate an axial force tending to urge, via a thrust-bearing means B, the cylinder drum 5 in the direction of arrow 11', i.e., against the control plate 2 and the floor 1b of the housing. The shoulders 23 and 26 are preferably formed by stepping the shaft 11 so that an intermediate boss 21 and a large boss 22 are formed in succession along the shaft and between the latter and abutment 12. To prevent leakage of the hydraulic medium from the annular chambers 24 and 27, we provide O-rings 29a, 29b and 29c flanking the chambers 24 and 27 and hugging the respective steps of the shaft 11. Between the inlet and outlet ports 10 and the respective chambers 24 and 27, we provide passages 25 and 28 to deliver the hydraulic fluid to these chambers at the low pressure of one of the ports and the high pressure of the other. Since the total pressure of these ports may remain substantially constant even though the differential pressure against the apparatus may be altered in accordance with the capacity and demand of the hydraulic system, the total force hydraulically applied to the shaft 11 in the direction of arrow 11' may remain constant, especially when the surfaces 23 and 26 have the same effective surface area. Thus the hydraulic force applied to the shaft 11 can be represented as If the surface areas A and A are equal, the total force F will be equal to the product of the sum of the pressure and the sum of the areas and independent of changes in pressure differential. To maintain a pressure of the cylinder drum 5 against the control plate 2 when the chambers 24 and 27 are depressurized, the spring washers 19 are employed as previously described. Inasmuch as the shaft 11 is nonrotatable with respect to the housing 1, the sealing of the chambers can be carried out with the O-rings 29a and 290 without concern as to wear of the sealing means.

In FIG. 2, we show a modified system wherein parts 110 are equivalent to the identically numbered parts of the device of FIG. 1. Here, however, the central shaft 30 is formed with a T-shaped abutment member 31 at its free end which is received in an annular compartment 32 open against a face of the cylinder drum 5. When hydraulic fluid is forced under pressure into the com- -partment 32, a lubricating and pressurizing film of the hydraulic medium is forced between the face 105 of the drum 5 and the juxtaposed face of the shaft 30 as will be described in greater detail below. The shaft 30 is, in this embodiment, provided with a stepped piston in the form of a sleeve 33 at the upper end of the shaft.

The sleeve 33 bears via an abutment flange 34 against the upper end of the housing 1 while a nut 35 is screwed onto a threaded end portion 30a of the shaft 30 and is of prismatic configuration complementary to the recess 35a in which it is received. The shaft 30 can thus shift axially within the housing 1 but is nonrotatably held therein by the snug fit of the nut 35 in the sleeve 33. Piston sleeve 33 is provided with a large-diameter portion 37 and a small-diameter portion 36 whose shoulders or pressurizing faces 37' and 36', respectively, are exposed to hydraulic pressure within annular compartments 38 and 40 of the housing. Passages 39 and 41 connect the chambers 38 and 40, respectively, with the ports while sealing rings 129a, 12% and 1290 are provided outwardly of the passages along the shaft 30 to prevent the escape of hydraulic fluid therefrom. A belleville or dished-washer spring 42 is provided between the housing 1 and the shaft 30 within the compartment 40 to retain, via the bearing means B, the cylinder drum 5 against its control plate 2 and/or the housing 1 even when the chambers 38 and 40 are unpressurized. The pressure chamber 38 is connected via a channel 44 in the shaft 30 with the compartment 32 while a similar channel 43 connects the pressurizing chamber 40 with this channel, check valves 45 being provided in these channels to prevent reverse flow of hydraulic fluid. Here, too, the cylinder drum 5 is mounted via needle bearings 20 upon the shaft 30. During a build-up of pressure in either of the chambers 38 or 40, the hydraulic pressure acts upon the respective annular faces 36', 37' to shift the shaft 30 in the direction of arrow 30 while fluid under pressure is forced into chamber 32 and between the juxtaposed faces 105, 130. The check valve 45 ensures that the pressure within chamber 32 will be maintained regardless of which of the chambers 38, 40 receives the higher pressure. The lubricant film between the juxtaposed surfaces thus constitutes a hydrostatic thrust means applying the axial force of the shaft 30 to the cylinder drum 5. The spring 42 is effective for this purpose when the entire system is depressurized.

While we have illustrated in both embodiments a system wherein two needle bearings 20 are provided between the cylinder drums and the shafts, it has been found that a single bearing means can be used advantageously for most applications. Thus alignment problems are avoided when a single bearing is employed and a limited freedom afforded the cylinder drum 5 to tip or cant with respect to the shaft 30; however, two sets of needle bearings permit higher speeds and greater torques.

We claim:

1. In an axial-piston machine having a housing, a cylinder drum rotatable in said housing and provided with an annular array of angularly spaced cylinder bores surrounding its axis of rotation, respective pistons slidable received in said bores, and a central shaft extending through said cylinder drum and rotatably journaling same in said housing, the improvement which comprises:

means on said housing supporting said shaft with at least limited freedom of axial movement in said housing;

means on said shaft and in said housing defining at least one pressure chamber in said housing at a location spaced axially from said cylinder drum and including at least one annular surface of said shaft pressurizable to shift said shaft in a direction tending to urge said cylinder drum against said housing, said chamber communicating with a source of elevated fluid pressure;

thrust means between said shaft and said cylinder drum for axially urging the latter in said direction upon the application of hydraulic-fluid pressure to said chamber; and

a control surface provided in said housing, said cylinder drum being provided with respective passages communicating with said bores, said control surface being formed with apertures selectively communicating with said passages upon rotation of said drum, said housing being formed with at least one inlet port and at least one outlet port for a hydraulic medium, said ports communicating with said apertures, said chamber being formed in said housing with said shaft at a location remote from said drum and behind said control surface, said shaft having a free end remote from said location, said thrust means including a face of said drum transverse to said shaft and antifriction means between said surface and said shaft, said shaft being retained in said housing against rotation relatively thereto, and said thrust means including an annular face at said free end of said shaft juxtaposed with said face of said cylinder drum, and means for feeding the hydraulic medium under pressure between the juxtaposed faces at said free end of said shaft to form said antifriction means.

2. The improvement defined in claim 1, further comprising at least one roller bearing rotatably supporting said drum upon said central shaft.

3. The improvement defined in claim 1, further comprising an annular axially effective spring surrounding said shaft and seated against said housing while yieldably bearing upon said shaft in said direction.

4. The improvement defined in claim 1 wherein a pair of said pressure chambers is provided in said housing beyond said control plate and remote from said free end, each of said pressure chambers having a respective one of said annular surf-aces pressurizable to shift said shaft in said direction, said chambers each communicating with a respective one of said ports, said means for supplying said hydraulic medium between said juxtaposed faces including a compartment formed at said free end of said shaft and opening between said juxtaposed faces, and at least one channel provided in said shaft and communicating between one of said chambers and said compartment, said chambers being sealed axially by O-rings flanking said chambers.

5. The improvement defined in claim 4 wherein a pair of said channels are provided in said shaft each communicating with a respective chamber and opening in common into said compartment, further comprising check-valve means for at least one of said channels for permitting flow of the hydraulic medium from the respective chamber into said compartment but blocking reverse flow therein.

6. In an axial-piston machine having a housing, a cylinder drum rotatable in said housing and provided with an annular array of angularly spaced cylinder bores surrounding its axis of rotation, respective pistons slidably received in said bores, and a central shaft extending through said cylinder drum and rotatably journaling same in said housing, the improvement which comprises:

means on said housing supporting said shaft with at least limited freedom of axial movement in said hous- 111g; means on said shaft and in said housing defining at least one pressure chamber in said housing at a location spaced axially from said cylinder drum and including at least one annular surface of said shaft pressurizable to shift said shaft in a direction tending to urge said cylinder drum against said housing, said chamber communicating with a source of elevated fluid pressure, said shaft extending through said drum over at least a major part of its axial length;

thrust means between said shaft and said cylinder drum for axially urging the latter in said direction upon the application of hydraulic-fluid pressure to said chamber and restrictive relative axial movement of the drum and shaft;

a control surface provided in said housing, said cylinder drum being provided with respective passages communicating with said bores, said control surface being formed with apertures selectively communicating with said passages upon rotation of said drum,

said housing being formed with at least one inlet port and at least one outlet port for a hydraulic medium, said ports communicating with said apertures, said chamber being formed in said housing with said shaft at a location remote from said drum and behind said control surface, said shaft having a free end remote from said location, said thrust means including a face of said drum transverse to said shaft and antifriction means between said surface and said shaft; and

an annular axially effective spring surrounding said shaft and seated against said drum while bearing upon said thrust means for yieldably urging said drum in said direction.

7. In an axial-piston machine having a housing, a cylinder drum rotatable in said housing and provided with an annular array of angularly spaced cylinder bores sur rounding its axis of rotation, respective pistons slidably received in said bores, and a central shaft extending through said cylinder drum and rotatably journaling same in said housing, the improvement which comprises:

means on said housing supporting said shaft with at least limited freedom of axial movement in said housing;

means on said shaft and in said housing defining at least one pressure chamber in said housing at a location spaced axially from said cylinder drum and including at least one annular surface of said shaft pressurizable to shift said shaft in a direction tending to urge said cylinder drum against said housing, said chamber communicating with a source of elevated fluid pressure, said shaft extending through said drum over at least a major part of its axial length;

thrust means between said shaft and said cylinder drum for axially urging the latter in said direction upon the application of hydraulic-fluid pressure to said chamber and restrictive relative axial movement of the drum and shaft;

a control surface provided in said housing, said cylinder drum being provided with respective passages communicating with said bores, said control surface being formed with apertures selectively communicating with said passages upon rotation of said drum, said housing being formed with at least one inlet port and at least one outlet port for a hydraulic medium, said ports communicating with said apertures, said chamber being formed in said housing with said shaft at a location remote from said drum and behind said control surface, said shaft having a free end remote from said location, said thrust means including a face of said drum transverse to said shaft and antifriction means between said surface and said shaft; and

a first thrust-bearing ring provided at the free end of said shaft, said thrust means including a second thrust-bearing ring disposed between said face and said first thrust-bearing ring, and bearing elements disposed between said rings, said housing being formed with a pair of said pressure chambers each having a respective one of said annular surfaces of said shaft pressurizable to shift said shaft in said direction, said housing being further provided with respective passages communicating between the respective chambers and respective one of said ports, said shaft being retained in said housing against rotation relatively thereto, each of said chambers being sealed by O-rings on opposite axial sides thereof,

References Cited UNITED STATES PATENTS 1,163,849 12/1915 Pratt 103l62 1,362,040 12/1920 Pratt 103l62 1,817,080 8/1931 Howard 103162 2,284,146 5/1942 Herman 103-162 2,987,006 6/1961 Bowers et a1 103-162 3,110,267 11/1963 Vetter 103162 3,124,079 3/1964 Boyers 103--162 3,188,972 6/1965 Thoma 103162 WILLIAM L. FREEH, Primary Examiner. 

